4.4.4 REPL Commands

The REPL exists to read expressions, evaluate them, and then print their
results. But sometimes one wants to tell the REPL to evaluate an
expression in a different way, or to do something else altogether. A
user can affect the way the REPL works with a REPL command.

The previous section had an example of a command, in the form of
,option.

scheme@(guile-user)> ,option value-history #t

Commands are distinguished from expressions by their initial comma
(‘,’). Since a comma cannot begin an expression in most languages,
it is an effective indicator to the REPL that the following text forms a
command, not an expression.

REPL commands are convenient because they are always there. Even if the
current module doesn’t have a binding for pretty-print, one can
always ,pretty-print.

The following sections document the various commands, grouped together
by functionality. Many of the commands have abbreviations; see the
online help (,help) for more information.